Recently, there have been proposed various methods of treating and recycling waste plastics, and further, parts thereof are practically employed. As a useful method of recycling and reusing such waste plastics, there is proposed a method and apparatus for gasifying the waste plastics by heating chips of the waste plastics in the presence of a decomposition catalyst of titanium oxide known as a photocatalyst under irradiation with ultraviolet light (See Patent Documents 1 and 2).
Further, catalysts used for decomposition treatment of the waste plastics chips have been variously studied (Patent Documents 3 to 5).
However, the decomposition apparatus using the above-mentioned decomposition method of waste plastics cannot conduct efficient decomposition treatment of waste plastics, and large treatment cost and a large apparatus are needed.
Further, the treatment of waste containing polyvinylchloride is known to generate a hydrogen chloride gas. Also, the treatment of Teflon™ is known to generate toxic hydrogen fluorides. The treatment of those kinds of gasses has become a problem.
Plastic and organic matter are difficult to treat on discarding them. Incineration treatment of them raises a danger of generating toxic substances such as dioxin.
In addition, pieces of plastic often contain metals such as aluminum and copper, and inorganic matter, and have metals deposited from the vapor or adhering to their surfaces, depending on their uses. If those pieces of plastic are incinerated, toxic gases may be generated or the incineration furnace may be damaged.
Accordingly, organic matter such as pieces of plastic is treated by landfilling in some cases. As plastics, however, the matter is not decomposed in the ground. In actuality, the availability of landfill sites has become difficult. Although there are biodegradable plastics, they have drawbacks of taking a long period of time until they are decomposed and of need of a very large area for biodegradation. Further, reusable metals, rare metals, and inorganic matter mixed in the waste plastic/organic matter cannot be separated therefrom, and they are simply landfilled or incinerated together with the waste plastic/organic matter.
Further, illegal dumping of industrial waste is a major problem.
There exists a conventional decomposition process for organic matter utilizing a catalyst. According to the existing process, organic matter such as plastics are crushed into granules in a crusher, and then the crushed organic matter is charged into a reaction vessel in drum shape, the reaction vessel containing catalyst granules in advance. After that, agitation blades are rotated in the reaction vessel to agitate the catalyst with the organic matter, while supplying hot air into the reaction vessel using a blower. The work of the catalyst enhances the decomposition of the organic matter, and thus the organic matter is gasified.
Although the catalyst is left behind in the reaction vessel, the gasified organic matter passes through a separator formed mainly of a cyclone dust collector, and only water vapor and carbon dioxide are emitted to the atmosphere as exhaust gases. By the above-mentioned gasification of the organic matter charged into the reaction vessel, new organic matter in an amount corresponding to the amount of the gasified organic matter can be charged into the reaction vessel, thereby allowing the above process to continuously operate without interruption.
The above existing decomposition apparatus, however, cannot conduct efficient decomposition treatment for waste plastics, and large treatment cost and a large apparatus are needed.
Further, the treatment of waste containing polyvinylchloride is known to generate a hydrogen chloride gas and nitrogen compounds. In addition, the treatment of Teflon™ is known to generate toxic hydrogen fluoride. The treatment of those kinds of gases becomes a problem.
In addition, a decomposition apparatus for waste plastics using a screw feeder to circulate a catalyst in a reaction vessel has been also disclosed (Patent Documents 6). However, under catalyst circulation using the screw feeder, the catalyst can wear out because of heavy load placed thereon. As a result of wearing of the catalyst, there is a problem of insufficient decomposition of waste plastics in a reaction vessel. Further, there is another problem of a shortened life span of the catalyst due to hard wearing of the catalyst, causing the need of frequently replacing the catalyst with new one in the reaction vessel. Further, the catalyst has been difficult in handling because of catalyst scattering.
In addition, in the catalyst circulation using a screw feeder, there is a problem of poor agitation efficiency of the catalyst and the waste plastics.
Regarding the prevention of secondary infection caused by infectious medical waste discharged from hospitals, dialysis facilities, and the like, a guideline specifying the treatment method of that kind of waste was issued from the Ministry of Health and Welfare on Nov. 17, 1989, and was enforced on Apr. 1, 1990. The guideline orders the hospitals, dialysis facilities, and the like to conduct in-house sterilization of the medical waste, in principle.
In this regard, there is wanted the development of a decomposition method and a decomposition apparatus for waste plastics, in particular the infectious medical waste containing polyvinylchloride, applicable in hospitals or clinics safely without using a large scale apparatus.    [Patent Document 1] JP-A-2002-363337    [Patent Document 2] JP-A-2004-182837    [Patent Document 3] JP-A-2005-066433    [Patent Document 4] JP-A-2005-205312    [Patent Document 5] JP-A-2005-307007    [Patent Document 6] JP-A-2007-8092